This invention relates to a cyclically operable signature machine in which signatures (folded sheets) are withdrawn from a supply hopper or magazine sequentially in timed relation and delivered to a signature gatherer, one atop another, eventually to complete a book.
Typical machines of the kind contemplated by the present invention are disclosed in U.S. Pat. Nos. 3,608,893 and 4,241,907, each of which discloses the operation of a so-called suction finger, controlled by a cam, for repeated oscillatory movement, successively to withdraw the leading signature from the supply hopper. However, in the instance of assembling the books on the basis of demographic standards, there may be instances where a signature is to be skipped or passed. As disclosed particularly in U.S. Pat. No. 3,608,893, the suction finger in such an instance will be latched in its advanced position quite close to the signature next to be delivered. There are instances where the latched state may prevail for several hundred cycles.
In more precise terms, the suction finger is mounted on a bell crank which has a cam follower spring biased against a continuously rotating cam responsible for synchronously operating the bell crank in accordance with the machine cycles. The sucker finger arm (or bell crank) carries a second roller, and when the suction finger is to be latched a notch in an actuated latching arm is presented to the second roller, capturing it and preventing return movement of the suction finger. Nonetheless, there must be allowance for some play in the latched position (a few thousandths of an inch). This is so in order that the latch can easily be released timely, and the cam follower accurately and gently returned to the cam contour rather than forcefully striking it.
This describes the latch disclosed in U.S. Pat. No. 3,608,893, with the understanding that the latching roller can be differently located, the notch of the latch differently configured and setting or actuation of the latch accomplished in different ways. The point is the suction finger is to be disabled, that is, prevented from oscillating when a signature is not to be withdrawn.
A thorough understanding of the background of the present invention also requires an explanation of the manner in which the signatures are moved forwardly in the supply hopper so that the forwardmost signature will be accurately positioned to the stroke of the suction finger. In achieving this, normal operation of the suction finger is accompanied by synchronous indexing (incremental movement) of a one-way clutch (or one-way pawl and ratchet as is sometimes used) which in turn is responsible for indexing a pair of roller chains or an equivalent infeeding conveyor to index the stack of signatures forwardly a few thousandths of an inch, compensating for the slack or space of each signature.
These synchronous movements and latching operations have proven to be eminently satisfactory in commercial practice, but if a there is a sparse supply of signatures in the hopper, such as in the instance of automatic loading, the resultant short supply can result in the latched-up suction finger and the one-way conveyor drive means opposing one another resulting in a jam due to the stack becoming too tight, too compacted. Thus, as mentioned above, the suction finger, even though latched, must be allowed to have a slight amount of motion (bell crank motion) under the influence of the cam. This motion or "play" is transmitted to the one-way clutch which indexes the conveyor a slight amount. As will be explained in more detail below, the latched-up finger will in fact nudge the forwardmost signature, because of the play, and repeated nudging can result in repeated operation of the one-way clutch, forcing the signatures forwardly at a time when none is to be fed.
The primary object of the present invention is to compensate the machine for low level or quantity of signatures in the supply hopper, thereby to prevent the stack of signatures from being compacted when the suction finger is latched.